1. Field of the invention
This invention relates generally to electrooptic scanners and more particularly to a monolithic electrooptic prism scanner using domain reversed regions for deflecting an incident light beam through a desired angle by applying an electric field to a body of electrooptic material.
2. Description of the Related Art
A particularly useful form of electrooptic scanner uses a series of prisms arranged in a line with alternating prisms oriented with their apexes pointing in opposite directions. A prism scanner of this type is described in Lotspeich, J. F. IEEE Spectrum, February, 1968, pp. 45-52. In his paper, Lotspeich describes the use of many identical discrete electrooptic prisms alternately inverted and arranged in a row to deflect laser beams by applying a voltage to a pair of parallel strip electrodes aligned above and beneath the iterated-prism array.
Even though discrete crystal or bulk deflectors such as the ones described by Lotspeich are useful, they are bulky and require high operating voltages. They are also expensive and difficult to integrate into systems that are manufactured in large quantities. To circumvent these disadvantages, deflectors which use planar or waveguide geometries have been developed. The field of integrated optics involves the integration of optical functions such as discrete modulators, interferometers, deflectors, and imaging elements on planar substrates. Many advantages can be realized from planar integration: compactness, multifunctionality, monolithic integration, and lower driving voltages. Planar versions of electrooptic prism deflectors have been disclosed in U.S. Pat. No. 4,614,408. Other related planar or waveguide electrooptic methods for deflecting light beams are described by Sarraf, Brophy et al., Stevens, and Makoto et al. Stevens uses arrays of electrooptic prism elements in waveguide structures, while Sarraf, Brophy, and Makoto et al. induce deflection of light beams by spatially modulating the refractive index of a waveguide.
In order to achieve electrooptically controlled prism structures in either bulk or planar format, some means for applying high electric fields must be provided. Heretofore, as shown in FIG. 1, sets of prism shaped electrodes were defined on the electrooptic material such that when properly activated, a change in the electric field is induced in the electrooptic material. It is desirable to use adjacent prism structures as shown by Lotspeich for bulk crystals, in a waveguide format in a monolithic device in order to increase the effective change in refractive index between adjacent prisms .DELTA.n, and thus the deflection angle. One difficulty inherent with this approach arises from the need to address adjacent prism electrodes on the monolithic device with voltages having opposite polarities.
As shown in FIG. 2, strong lateral electric fields are created between adjacent electrodes which can lead to electrical breakdown, the creation of inefficient tinging fields, the need for complex voltage interconnects and, in some cases, the need for bipolar voltage sources. These problems may be somewhat reduced by applying a voltage to every other prism electrode and not applying any electric field to their immediately adjacent prism regions. In order to achieve higher deflection angles, however, it is desirable to increase the effective .DELTA.n across an interface by applying opposite electric fields between adjacent prism electrodes which are antiparallel in direction. In this case, the effective change in refractive index between adjacent prism regions with antiparallel electric fields is 2.DELTA.n, twice that of the single polarity case.
Although the antiparallel field type of planar prism deflector may be used, it is prone to electrical breakdown, requires complex electrode structures and electronic interconnects, and produces inefficient tinging fields between adjacent electrodes. In some instances, the distance between adjacent electrodes may be increased to minimize breakdown and tinging fields. Unfortunately, this approach is inefficient since it does not fully utilize the electrooptic material. On the other hand, if only every other prism is activated (single polarity case), only one half the deflection angle may be achieved. This is not very desirable since the number of resolvable scanned spots is approximately proportional to the scan angle. Higher voltages may be applied to compensate for the factor of two loss in scan angle, but high speed modulation becomes increasingly more difficult and expensive as the voltage increases. Higher voltages can also lead to material breakdown, charge injection, electrode deterioration, and saturation effects.
In summary, existing electrooptic prism deflectors exhibit several shortcomings which can limit their application and utility.